Plant for processing of refuse material

ABSTRACT

A plant for the processing of domestic refuse material has feeding and shredding means, digester means and separating and grinding means. The feeding and shredding means shred the entire refuse material and feed it without sorting to the digester means. The digester means include at least one digester having a plurality of open cells provided with air and water to support aerobic degradation of the refuse material. Control mean regulate the passage of the material from cell to cell and also regulate the supply of water to the material in the cells to control the moisture content of the material leaving the digester. The separating and grinding means are located after the digester means and are used to remove metal objects form the degraded material and thereupon to reduce the degraded material to fine pulverulent form.

llnited States Patent {72] Inventor William Watson Kirk The Saddlers, Wooton, Quatt. near Bridgnorth, England [21] Appl. No. 735,490 [22] Filed May 16, 1968 [45] Patented Nov. 23, 1971 [32] Priorities June 1, 1967 [33] Great Britain [31 25,228/67;

Aug. 31, 1967, Great Britain, No. 39,770/67; Feb. 6, 1968, Great Britain, No. 5,774/68 [54] PLANT FOR PROCESSING OF REFUSE MATERIAL 13 Claims, 10 Drawing Figs.

[52] U.S.Cl 210/105, 210/142, 210/152, 210/223 {51] Int. Cl B01111 50/00 [50] Field of Search 210/152, 173,222,223, 220, 221, 105, 142

[56] References Cited UNITED STATES PATENTS 2,094,909 [0/1937 Baily et a1. 210/152 X 2,246,224 6/ l 941 Streander 210/152 2,360,811 10/1944 Kelly 6! a1 210/152X 3,257,081 6/1966 Brown et a1 210/152X 3,471,020 10/1969 Wallace 210/152 Primary Examiner--.l. L Decesare Anorney-Richards & Geier ABSTRACT: A plant for the processing of domestic refuse material has feeding and shredding means, digester means and separating and grinding means. The feeding and shredding means shred the entire refuse material and feed it without sorting to the digester means. The digester means include at least one digester having a plurality of open cells provided with air and water to support aerobic degradation of the refuse material. Control mean regulate the passage of the material from cell to cell and also regulate the supply of water to the material in the cells to control the moisture content of the material leaving the digester. The separating and grinding means are located after the digester means and are used to remove metal objects form the degraded material and thereupon to reduce the degraded material to fine pulverulent form.

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. large hopper sufllcient 1 PLANT FOR PROCESSING OF REFUSE MATERIAL refuse from offices, shops, meat and vegetable markets and the likeQbut it does not refuse.

In the past there have been several approaches to the problem of the disposal of such domestic refuse, the simplest of which beingtipping, but this gives rise to spontaneous cominclude heavy or chemical industrial .bustion, foul odors and a general health risk due to the proliferation of pests such as rats and flies.

It is also known to incinerate such refuse prior to tipping in order to reduce the health risk and to reduce'arid stabilize the amount of material to be tipped.

However, for some time it ,has been appreciated that such refuse is basically a mixture of biologically degradable matter as vegetable mattenariimal matter and for some part paper; and biologically unsuitable matter such as'tin cans, bottles, a"shes, plastics materials andthe like, and efforts have been'made to utilize the degradable matter for the production of a material having some usefulness as a compost. To do this it has been'proposed to allow the refuse to rot, water being and thereupon the partially rotted mixture has been separated or screened to removed the moist compostlike material'fror'n the remainder. However, this yields only a small proportion of compost material and a large remainder which has to'be tipped or incinerated.

lt has-been proposed to improve this process by utilizing a plant wherein the domestic refuse is tipped into a large hopper from which it is gradually fedon to'a picking belt which passes several picking stations wherein operatives remove large objects, unsuitable objects such as bottles and the like and ferrousmetal objects, the remaining material being fed gradually to a shredder and from=the shredder to vessels wherein it is allowed to rot, after admixture with water. The rotted material is then screened so as'to separate out the particulate compost material, all particles above a certain minimum size being rejected for tipping along with'all the material picked out, except of course for the ferrous metals.

This system has many disadvantages in that it requires a to hold a day's refuse collection in which the material may choke before it can be gradually discharged. It requires the presence of operatives in order to supervise and control thematerial to ensure proper discharge of the material fromthe hopper.'Also,if the" picking is not performed efficiently the shredder can be choked and even damaged, and the use of labor for picking is expensive. The use of vessels operating at a given speed irrespective of load was found not-to yield a product of reliable characteristics and therefore the quality of the compost material can vary between wide and unacceptable extremes both in so'far as its handling characteristics are 'concemed and in so far as its qualities as a compost are concerned. Furthermore, the amount of rejected material screened from the compost material is large and the plant therefore converts only 'a relatively small proportion of the domestic refuse into compost material, which after further essential treatment is suitable for agricultural use.

The present invention has for an object, the provision of plant which will obviate the aforementioned disadvantages, and a further object is to enable a very large proportion of the domestic refuse to be converted directly into a material having the qualities of a fertilizer, which is commercially much more acceptable than'a compost material, both in so far as the handling of the material is concerned and in S far as the horticultural or agricultural performance is'concemed.

A further object of the invention is to reduce to an absolute minimum the number of operatives required and to obviate the most distasteful manual handling, e.g. picking of the raw refuse.

A further object of the invention is to enable the process to be carried out continuously so as to be substantially independent of refuse collection schedules.

material is shredded and from which digester means comprising one or more A further object of the invention is to provide a plant which is reliable and which is able to take the complete range of usual domestic refuse including, for example, large objects such as chairs, without the need for preeorting or picking.

A further object of the invention is to enable the amount of material to be tipped to be kept at an absolute minimum and to render such material into a state that it is not distasteful to handle or which is a health risk when tipped.

A further object of the invention is to convert domestic refuse into a granular or pulverulent and easily handable stable fertilizer composition or product which may be bagged or packaged directly for sale, and may be stored either packaged or in bulk without significant deterioration.

To facilitate the biological digestion and degradation breakdown of the refuse within the plant an object of one particular form of the invention is to provide digester means wherein the shredded or broken up domestic refuse may be kept under controlled conditions until such breakdown is effected, by reacting the material with water and air. In particular, the digestermeans is provided with novel control .means whereby to regulate theconditions within the digester means; whereas the prior known vessels or devices into which the material was tipped have no such means so that the breakdown of the material cannot be accurately and variably controlled.

Other objects of the present invention will become apparent from the following detailed description.

By means of the present invention a. plant for the treatment of domestic refuse can be provided which-is arranged to guide or feed the refuse as it is tipped from a collection vehicle by first or slow feed means on to a fast feed means which conveys the material to a high-capacity shredder wherein all the the material is fed to digesters, the digester means having control means which ensures that the amount of water and air supplied to the material is supplied under controlled conditions as is the rate at which the material is progressed through the or each digester from cell to cell therein, the maximum rate of progression being determined by the. rate at which decomposition takes place and not by the rate at which material is fed into the digester; further conveyor means take the digested material from the digester means to a pulverizer or grinder wherein the material is rendered substantially into a fine granular state, and from which the material is dischargedand conveyed to screening means so as to remove the small proportion of material which has passed through the v pulverizer or grinder without being reduced below the size required.

By this means it has been found that a major proportion of the refuse material can be converted directly into a fertilizer composition of fine soillike consistency which has a controlled moisture content and which may be blended with additives if desired before sale, and that there is only a very small proportion of oversize material to be disposed of by tipping.

According to the present invention there is provided a plant, for the processing of domestic refuse material, comprising feeding and shredding means, digester means comprising at least one digester providing a plurality of open cells having waterand air supplies, control means to regulate the passage of material through the said digester means and to regulate the supply of water to the material in the cells in order accurately to control the digestion, degradation or breakdown of the material and to control the moisture content of the reacted material leaving said digester, the air supply being arranged to ensure that an excess of air is supplied to the material in the cells, and means for subsequently separating and grinding said within the tower a superimposed series of intercommunicatin g digester cells.

The invention further provides a process comprising the steps of shredding domesticrrefuse material, reacting the material with a known amount of water and with a known air supply, sensing the temperature rise, further reacting the material with addition of controlled amounts of water and an excess of air so that the material is biologically digested, degraded or broken down while advancing and tumbling the material from one level to another at intervals during the reaction, and separating and grinding the reacted material.

The invention will now be described in further detail with reference to the accompanying drawings which illustrate an example of the plant and process, and wherein:

FIG. I is a schematic block diagram showing the major units and material flow in the plant;

FIG. 2 is a diagrammatic sectional view of feeding and shredding means of the plant;

FIG. 3 is a similar diagrammatic elevational view of digester means of the plant;

FIGS. 4 and 5 show separating and grinding means of the plant in elevation and plan view;

FIG. 6 is a temperature diagram;

FIG. 7 shows diagrammatically a control means;

FIGS. 8 and 9 show additive blending means of the plant in elevation and plan view; and

FIG. 10 shows packaging and storing means of the plant, in plan view.

As shown diagrammatically in FIG. 1 the plant for the processing of domestic refuse material constructed in accordance with the invention comprises two parallel lines of primary treatment plant which are linked to a common after treatment plant.

Each line of primary treatment plant comprises feeding and shredding means indicated by reference numeral 1, digester means indicated by reference numeral 2, and separating and grinding means indicated by reference numeral 3.

The after treatment plant comprises additive blending means indicated by reference numeral 4 and packaging and storage means indicated by reference numeral 5.

The primary shredding and feeding means 1 comprises a main slow feed hopper I01 and a secondary slow feed hopper 102 which each discharge into a fast feed hopper 103 which carries the raw refuse material past a primary metal detector 104 to the primary shredder 105 from which the shredded material is discharged into a further hopper 106 provided with an expansion chamber (FIG. 2).

The shredded material is then conveyed over a rate weigher 201 to the digester means 2 which comprises a series of 12 digester towers 202 into which the material is distributed by a two-level vibratory conveyor 203.

The digested refuse material is conveyed from the digester means 2 to separating and grinding means 3 comprising an overband magnetic separator 301, a metal detector 302 and a primary screen 303 which overlies a secondary grinding or crushing machine 304. The finely ground material from the crushing machine 304 is screened by a vibratory conveyor screen 305 and the fine crushed material which passes through the screen is discharged on to another conveyor 306.

The material from both of the separating and grinding means 3 is discharged on to this conveyor 306, which takes the material via a rate weigher 403 to the additive blending means 4 which comprises hopper-feeding devices 401,402 from which additive materials are added to the material on the conveyors 306 to produce an augmented or enriched fertilizer material. This fertilizer material is then blended and conveyed to the packaging and storage means 5, which comprises bagging machines 503,509 and a bulk storage silo 517.

As shown in FIGS. 1 and 2 the primary shredding and feeding means 1 for each line of primary treatment plant are housed together in a reception building which provides a reception floor 107 upon which vehicles can be maneuvered to enable them to tip the raw refuse material into any one of the four slow feed hoppers 101 and 102, the primary shredding and feeding means of one line of primary treatment plant being offset diagonally of the building so as to enable its discharge elevator conveyor 108 to bypass the other primary shredding and feeding means 1 which is shown in broken outline in FIG. 2.

The slow feed hoppers 101 and 102 are provided with an enclosure 109 in which an opening 110 is provided to accommodate the rear end of a refuse collection vehicle. A buffer or stop 111 is provided to prevent vehicles from reversing over the edge of the floor 107. As shown, the wall of the building is provided with a ramp face 112 to prevent material overshooting the sides of the slow feed hoppers 101 and 102. These slow feed hoppers 101 and 102 are of equal size and are arranged to feed material directly into the fast feed hopper 103. However, controls are provided to enable the main slow feed hopper 101 to govern the rate of feed of the secondary slow feed hopper 102 so that, if necessary, the rate of feed of the secondary hopper 102 can be arranged to be dependent upon the rate of feed of the main slow feed hopper 101. This arrangement may be obtained by sensing the load upon the motors driving the jigging mechanism of the main slow feed hopper, said sensors actuating the motor controls of the secondary slow feed hopper, so that, in use, material of readily degradable nature such as the refuse from slaughter houses and vegetable markets can be stored in the secondary slow feed hopper and used to blend with the material flowing from the main slow feed hopper 101 if such material is for example predominately predominantly composed of paper, ashes, and like materials.

Where the material is from domestic households and already contains food scraps and the like both slow feed hoppers 101 and 102 may be used simultaneously to discharge the material at full speed into the fast feed hopper 103.

The fast feed hopper 103 is also a jigging hopper which transports the material to the infeed chute 113 of the primary shredder 105. Situated in an upper part of the fast feed hopper 103, adjacent the infeed chute 113, is the metal detector 104 which is set so as to detect only very large lumps of solid metal for example, a blacksmith's anvil weighing more than approximately 150 pounds.

The metal detector is coupled of the controls to the power supplies for the motors driving the fast feed hopper and the shredder 105, so as to be able to halt these machines should a very large metal object be detected.

A door or hoist hatch, not shown, to provide access to the fast feed hopper 103 is provided to enable such very large metal objects to be removed, and the release mechanism of the door or hoist is provided with an automatic safety lock which prevents operation thereof until such time as the large primary shredder 105 has come to a halt.

It is to be understood, that the primary metal detector 104 is provided as a safety device in case the refuse material should accidentally contain a very large metal object; it is not the function of the metal detector to stop the primary shredding and feeding means 1, should usual metal objects and sheet metal fabrications such as tin cans, toy vehicles, perambulators, refrigerators or bicycles and like domestic rubbish be present.

The primary shredder 105 is arranged to shred all material fed through it and to this end its drive motor is of approximately to 200 or more horsepower per 100 tons per day of the line of primary treatment plant, and from the drawings it will be obvious that the primary shredder will have a capacity sufficient to shred a day's material throughput in approximately 6 to 8 hours.

The shredded material from the shredder 105 is discharged into the further jigging hopper 106 which is provided with an expansion chamber 114 to allow the airflow generated by the shredder to be slowed down so that it no longer entrains particles of refuse material, such as paper shreds, before the air flow is discharged through an outlet screen or duct (not shown) provided on an upper surface of the expansion chamber.

The material from the further hopper 106 is discharged on to the elevator belt conveyor 108, which carries the shredded material up to the digester means 2 (FIG. 3). As s shown in FIGS. 1 and 33, in eachline of primary treatment plant, the material is transported by the elevator conveyor 108, and is passed over the rate weigher 201 which incorporates or is electrically connected to a weighing device A (which forms part of control means as described hereinafter with reference to FIG. '7 The weighed material is then further carried by the conveyor 108 and is dropped on to the upper run 204 of the two-level vibratory plate conveyor 203.

This upper run 204 incorporates pivotally mounted plates 205 which are pivotable between a position wherein they complete the upper run 204 so that material is transmitted thereon and a position wherein they interrupt the upper run so that material is allowed to fall on to a lower run 206 of the conveyor.

As shown in FIG. 3 there is one pivotable plate 205 disposed above and immediately preceding each digester tower 202, and the lower run comprises a series of plates 206, there being one plate for each pivotable plate 205. The plates 206 are each cut away so as to taper in width where they overlie the open entrance 207 of the respective digester so that material passed to the plates 206 is distributed so as to fall on to a first shelf 208 of the digester tower adjacent a first pusher 209.

As shown diagrammatically in FlG. 7 each tower 202 is generally rectangular and is of sheet and girder metal construction so as to be provided with the upper inlet 207 and a lower outlet 210. Between the longitudinal walls 211 of the tower 202 are a series of seven shelves of which the first shelf 208 provides a test area 212 and a first reaction area 213, then follow five further reaction shelves 214, which each provide four further reaction areas one of which is indicated by reference numeral 215, and at the bottom of the tower there is a discharge shelf 216. These shelves, 208, 214i and 216 define within the tower 212 a vertically stacked series of intercommunicating or open digester cells.

The first shelf 208 is attached by its upper end 217, beneath the inlet 207, to one of the lateral walls 218, from which it extends transversely down towards the other lateral wall 218, so as to leave a space2l9 between the lower or free end 220 and said lateral wall 218.

The second shelf 214 extends from the lateral wall 218 so that the corresponding space 221 lies above the upper end of the third shelf. The subsequent shelves 214 are similarly alternately arranged except in that the corresponding space provided at the lower end of the last or discharge shelf 216 serves as the outlet 210 from the tower.

The first shelf 218 is provided with an air supply line 222 so that compressed air can be supplied to the test area 212 through aeration ports (not shown) provided in the shelf.

Similar air supply lines 223 and 224 are provided for the reaction areas 213 and 215 so that each reaction area gets a resective supply of compressed air.

While the shelves have been shown as simple downwardly inclined sheet metal structures, it is to be understood that it is possible to provide on the shelves various inclined planes, ramps or steps so that the material is caused to tumble as it passes the aeration ports. It is also to be understood that the air supply lines 222, 223, and 224 may terminate in plenum chambers provided below or above the shelves, e.g. in the form of hollow steps, so as to further distribute the air across the width of the shelf, the aeration ports being provided in appropriate surfaces of the plenum chambers.

Controlled valves are provided in each air supply line for control purposes as hereinafter described, and thereafter the air supply lines join a common air feed line disposed in trunking 225 running vertically up the longitudinal walls 211 of the tower 202 (see FIG. 3).

The test area 212 is provided with a series of water spray jets from a water supply line 226, which supply line is provided with a valve (not shown) in order that the flow of water to the jets may be controlled as hereinafter described.

Similarly, the first reaction area 213 is provided with a serics of water spray jets supplied along a line 227 which is also provided with a valve. Further water supply lines 228 are provided to supply sprays situated above each of the further reaction areas 215, each supply line having a respective valve.

All the water supply lines are connected to a common constant pressure water main which runs up the side of the tower within the trunking 225.

Each shelf 208,214,216 is provided with a respective pusher 209,229,230 and each pusher is actuated by a hydraulic ram (not shown) controlled by the control means as hereinafter described.

The first pusher 209 is arranged to have a total operating stroke of approximately the length of the first shelf so that it can push the materials beyond the test area 212, whereas the pushers 229 have a stroke of approximately a quarter of the length of the tower, LE. equivalent to moving the material by distance of approximately one reaction area, after suitable allowance for compression of the material has been made. The last pusher 230 has an operational stroke substantially equal to the length of the shelf 216 in order that this shelf may be completely cleared of material; The motive power for the rams, whether hydraulic, as described, or pneumatic or electrical, is conducted by conduits arranged within the trunking 225.

Temperature probes are provided for each shelf in positions in which they will contact the material on the shelves, the temperature probes for the first reaction area 213 being indicated by reference numeral 231, similar probes 232 being provided for the subsequent reaction areas 215.

However, in the test area 212 the temperature probes 233 (shown diagrammatically in FIG. 7) are provided in several rows each comprising several probes so that an accurate mean temperature can be obtained for the material in the test area. It is to be noted that these probes 223 extend to adjacent the shelf; they are shown diagrammatically in FIG. 7.

In operation, the pushers may be actuated in either daytime or nighttime modes, the modes varying generally in that dur ing the daytime the pushers will be advanced by distances corresponding to the length of a reaction area, whereas during nighttime operation the pushers may be advanced in increments until a complete stroke is reached, and during the nighttime mode the last pusher 230 will be arranged so as to allow material to accumulate on the last shelf 216 to prevent material being discharged from the tower 202, whereas during the daytime the material will be discharged from the shelf 216 whereupon it will leave the outlet 210 on to a discharge conveyor 234, which is of jigging plate type.

It will be appreciated from the foregoing description and drawings that the material will be fed gradually along the shelves so as to fall through the spaces 219,221 on to the next shelves, thereby causing the material to be mixed but the pushers, being of full width, will prevent uneven distribution of the material on the shelves.

Also, by using a jigging plate-type discharge conveyor, the effect of discharge surges will be minimized. The discharge conveyor 234 transports the material from the towers to an elevator belt conveyor 235.

At the discharge 210 of each tower there is a reject discharge mechanism 236, one form of which is shown in FlG. 7, by which, as hereinafter described, material may be diverted from the discharge conveyor 235 to a reject conveyor 237, which returns such rejected material to the elevator conveyor 108 for reprocessing as shown in H0. 1.

It is to be understood that the tower may have any number of shelves of any desired slope or no slope providing any number of reaction areas from one upwards, as is desirable under pertaining conditions, but the size should be limited to reduce the compaction of the material as it is progressed, and any suitable means may be provided to progress the material through the tower. Also, any suitable number of towers may be provided for the digester means The elevator conveyor 235 transports the digested material to the separating and grinding means 3 shown in FIGS. 4 and 5.

Before the material leaves the conveyor 253 it passes beneath an overband magnetic separator 301 which removes magnetic materials and drops them through a chute 307 to an automatic scrap-baling machine 308.

The material is then carried beneath a metal detector 302 which is set so as to detect lumps of metal of a size greater than 5 grams. After passing the metal detector 302 the material is tipped into the intake funnel 309 of the secondary grinding or crushing machine 304 driven by a motor of approximately I to 200 or more horsepower per I00 tons daily rated capacity of the line of primary treatment plant.

As the material traverses the intake funnel 309 it is forced to pass through the primary screen 303 which comprises an array of parallel inclined bars which are spaced apart by about 2-3 inches so as to remove, for example, large pieces of rubber tire, which roll down the screen to a disposal chute indicated by reference numeral 310.

Should the metal detector detect a piece of metal then it will cause a pivotally mounted arm 311 to swing so as to interrupt the material as it falls into the funnel 309, the swing being timed so as to take out that portion of the material which contains the metal object. The arm 311 then rotates to a position overlying the primary screen 303 which comprises an inclined metal plate. At this point the arm 31] is actuated so as to drop the portion of the material on to the inclined plate, and from there the material slides or rolls down the plate over a series of perforations 312 therein which pennit the fine material to fall into the funnel while causing the metal object to continue moving until it falls into the chute 310. The arm then continues to rotate to the initial position shown in FIG. 5, wherein it is clear of the funnel. It is to be noted that the arm may be provided with any suitable sort of scoop or enlargement to catch material. Alternately, an air blast mechanism or a movable deflector plate may be provided to deflect metal objects to fall into the chute 310.

The grinder 304 reduces a very large proportion of the digested material to a fine pulverulent state and the fine material is discharged from the grinder 304 on to the two level vibratory screen conveyor 305, which comprises an upper perforate screen which overlies a sheet metal trough 313 which, because it is jigged, acts as a conveyor, which conveys the flne material passing through the screen to the common product conveyor 306, which leads to the after treatment plant.

The upper perforate screen is interrupted by a deflector plate 314 which deflects any oversize material to a chute 315. As shown in FIGS. 4 and 5 the chutes 310 and 315 from both lines of primary treatment plant discharge on to a common disposal conveyor 316, of belt type, for transporting the oversize material and for tipping. It is to be understood that the disposal conveyor 316 need not be single conveyor but could be duplicated so that the metal objects can be collected separately for separate disposal, as the scrap may be of value, or such conveyor 316 could be dispensed with and hoppers or bins provided to collect material from the chutes 310,315.

In an alternative embodiment the reject discharge mechanism 236 is transferred from the discharge or outlet 210 of the tower 202, and a reject mechanism comprising a pivotal deflector 317 is provided to deflect material to be rejected from the trough 313 onto a reject conveyor 318, one such mechanism being shown in FIG. 5.

Such reject conveyor 237 or 318 may return material to the slow or fast feed hoppers 101, 102 and 103. In this example the operational control means comprises a master plant control unit and a respective digester control unit for each digester, the digester control units being connected to the master plant control unit so that their overall function may be determined by the master unit. The master plant control unit has data supplied thereto by each digester control unit, and its operation may be controlled by the persons supervising the plant so that once the basic mode of operation of the plant has been selected by the operatives or supervisors the plant can run substantially automatically and make automatic compensation for the various changes which may occur in the operating conditions.

In particular, and with reference to FIG. 6 which shows three hypothetical curves, in diagram form, for three different refuse compositions, each digester control unit is arranged to receive data from the weighing machine 201 associated with the line of primary treatment plant and instructions from the master plant controller, and thereafter cause a predetermined proportion of water to be sprayed onto the material as it enters the digester tower 202 and to supply the material as it rests upon the test area 212 of the first shelf 208 with a known and predetermined flow of air, and to receive data from the thermometers 233 indicating the initial temperature rise (on scale 1) of the material to time T1 from which the first part of the diagram can be obtained, and from this first part of the diagram the slope thereof will give an indication as to the inherent rate at which the material can be degraded.

Once this degradation, decomposition or reaction rate has been determined, and it is this rate which is the important characteristic of the material in so far as the degradation thereof is concerned, the digester control unit will select a matching program and it will thereafter control the supply of water and air to this particular portion of material as it progresses through the digester so that the temperature thereof follows the correct curve until time T2 whereat the material is ready for discharge.

To this end as shown in FIG. 7 each digester control unit comprises a number of electronic devices which are schematically indicated in the figure under respective reference letters according to the following key:

The Weighing Device; The Conversion Device; The Primary Water Flow Control; The Primary Air Control; The Temperature Test Device; The Characteristic Calculator; The Program Selector and Actuator; The Shrinkage Correction Unit; Secondary Shrinkage Correction Unit; The Summation Unit; The Conversion Unit; The Pusher Control Unit; The Secondary Water Control Units; The Secondary Water Control Unit for the First Reaction Area 213; The Second to Fifth Secondary Water Control Units for the Second to Fifth Reaction Areas 215; The Secondary Air Control Units; The Secondary Control Unit for the First Reaction Area; MZ-S, The Secondary Air Control Units for the Second to Fifth Reaction Areas; N The infeed Conveyor Unit; D. The Product Reject Control Unit; XL. The Supplementary Water Control Unit;

The Alarm System; M. The Master Control Unit; OL. The Data Logging Unit; and CW. The Check Weighing Unit:

The weighing device A. is attached directly to the rate weigher 201 which weighs the material as it is fed along the conveyor 108 to the digesters, and the weigher A. transmits corresponding weight signals to the master control unit M. The master control unit then generates signals which are fed to the weigher A. and to the conveyor control N. so that the conveyor 203 is actuated so as to feed material into the appropriate digesters, in such a manner that each tower receives a standard sized batch of material in several portions, and after each portion the conveyor control N. signals the master control M. which levels off the portion by causing a small reciprocation of pusher 209, and signals are transmitted to the conversion device B. of the digester control means of the appropriate digester. On receiving a signal the conversion device B transmits signals strictly proportional to the weight of material fed into the digester to the primary air and water control units D. and C. respectively which open valves or throttles to cause a predetermined amount of water to be sprayed on to the material and to cause a predetermined rate of air flow to be fed to the material.

When the batch is complete it is advanced to the test area 212 by pusher 209, the-air supply being maintained and further water being added if necessary to complete the predetermined'amount.

The unit B. also transmits signals to the date logger to provide a record of the amounts of material, water and air.

The temperature test device continuously senses the temperature of the material in the test area 212 by means of probes 233, and feeds corresponding signals to the calculator F. At a predetermined interval after the air and water has been supplied to the material in the reaction area the master control unit causes the calculator to start and after a further delay to stop a summational calculation of the temperature increase or signals provided by unit B. At the end of the calculation a coded signal corresponding to the temperature increase is transmitted to unit G. which also receives a weight signal for the batch and which then selects a matching program.

This weight signal may come from unit B., as shown, or from the master control unit. However, should the temperature rise be less than a predetermined minimum the program selected will be a reject program and when the material has passed throughthe digester the product reject control unit 0. will be signalled to actuate the reject discharge mechanism 236 or 317. Under normal circumstances however a working program will be selected and allocated to this particular batch of material.

When this batch of material has been advanced by the pusher 209 from the test area to the first reaction area the unit G. will be actuated as hereinafter described and will transmit a signal to unit L1. which will in turn cause a volume of water determined by the program in unit G., to be sprayed on to the material. At the same timea similar signal will be sent to unit M1. which will actuate a throttle or valve so as to ensure that air is supplied to the material in the first reaction area 213 at a rate corresponding to the program. Also, the unit G. will transmit a corresponding signal to the data logger in order to provide a record of the amounts of water and air fed to the material in accordance with the program. Similar signals will be sent to units L. and to all units M. for all reaction areas 215 on all five shelves 214 by the unit G. in accordance with the programs previously selected for the batches of material-in the corresponding reaction areas.

All reaction areas 215 are provided with temperature probes and, as shown in FIG. 7, the probes in the first reaction area 213 are connected to unit M1. so that should the tem perature vary from thedesired temperature stipulated in the program, the unit M 1. will automatically vary the rate at which air is supplied to the material. Under certain circumstances it may also be desirable to add further'water, e.g. should the temperature fall below that determined by the program, and to this end, the temperature probesmay further be connected to unit L1 as shown in dotted line in FIG. 7. Again, while certain variations in the amount of water supplied to the material may not afi'ect the subsequent processing of the material a further feedback loop is provided between unit L1. and the unit G. so that, if necessary, the particular batch of material may be allocated a different program.

Such circumstances could arise in an instance wherethe coded signal corresponding to the temperature lay just within the limits of a particular program whereas the material might actually require the next adjacent program.

Subsequent temperature probes 232 are similarly connected to the corresponding units L. and M. for subsequent reaction areas.

Throughout the digester control system the units D. and L. only vary the amount of air which is in excess of the theoretical amount necessary to support aerobic degradation or decomposition or digestion of the material, the primary means of regulating the temperature being the regulation of the supply of water as laid down in the program selected for the batch of material.

Under normal working conditions and except as hereinafter described, the pushers are actuated starting with pusher 230 and upon completion of the advance of this pusher the next pusher 229 and so on until the first pusher 209 has completed its stroke and has been withdrawn. This sequence is controlled by unit K., the pusher control device, and the sequence is started by a signal from the master control unit fed to the unit K. Provided on each pusher is a sensing device, as described, which transmits signals strictly proportional to the amount of movement of each pusher to the summation unit 1. which receives these signals and sums the total'progression of the materials through the digester upon completion of the sequence of full strokes intitated by unit K. As described, the pushers may be actuated either in whole strokes or else in partial strokes, and in the latter instancethe unit I. will sum up the partial strokes until a complete stroke of each pusher has been completed. Upon completion of the strokes the unit I. will transmit a signal to the conversion unit J. which will in turn transmit signals to the data logger and master control unit M. as a check that the pusher sequence has bee completed, and will transmit a further signal to the unit G. so that the program may be followed by the batches which will all have been advanced by one reaction area. By this means the programs are kept in sequence with the progression of the material through the digester so that the units L. and M. at all times follow the correct programs Under certain circumstances it may be necessary to provide a correction factor for the shrinkage of the material and in such instances the movement of the first pusher 209 is transmitted to unit H. which in turn transmits a corrected signal to the summation unit 1. Again under certain circumstances the unit H. may be required together with a second shrinkage correction unit H2. to which the signals from the second pusher 229 are directed, so that corrected signals from both correction units H. and H2. may be transmitted to the summation unit I.

Associated with the various temperature-sensing devices 231, 232, 233 are connections to the alarm system P., in case of emergency such as fire, such an alarm system being provided purely as a safety measure.

Provision is also made for a signal to be sent from the conversion device B. or master control unit M. to the program selector G. in the event of a batch of material being below the weight limits prescribed for normal batches, to enable the program for that batch to be modified accordingly.

The master plant control unit, which is not represented except insofar as the connections thereto from each digester control unit are concerned, is primarily concerned with the timing of the various operations of the several digester control units and with the changeover between daytime and nighttime modes of operation of the plant.

During the daytime mode the operation of the master and individual digester control units is asdescribed hereinbefore, but at the end of a working day, the. persons supervising the plant can, by actuating a switch arrangement of the master control unit, shut down the feeding and shredding means and the conveyors 108 and 203 thereby initiating the nighttime mode of operation wherein units A. and N. are switched off as they effectively form part of the .master control unit, and the signals to the unit K. are altered so that the pushers act only in fractions of strokes and/or at less frequent intervals so that material in the tower will be advanced by one or possibly two reaction areas during the course of the night.

Since there is no infeed to the tower-phasing signals may be transmitted from the master control unit to the unit G. so that if necessary one or more of the signals from the unit 1. may be cancelled in the instances lwhere the pushers make void strokes over areas from which the material has already been moved.

During weekends, public holidays and like shutdown periods wherein there is no refuse collection, a modified form of the nighttime mode of operation is provided by the master control unit wherein the pushers are actuated at much larger time intervals, and wherein further signals are transmitted by the master control unit to each of the units G. whereby to initiate the changeover to modified programs to ensure that water evaporated from the material is replaced.

When reverting to the daytime mode of operation fresh material is allocated to each digester in turn, and this material will be advanced as described until it reaches the material already present whereupon all the material will subsequently be advanced together.

At the end of the nighttime mode the discharge shelf 216 will require clearing, and to this end on changing over to the daytime mode the master control unit will send a signal to the unit K. of each digester, in turn, whereby to actuate the pusher 230 to clear the shelf 2l6 thereby to discharge the digested material from each tower in turn so as not to overload the conveyor 234. This discharge procedure is carried out independently of the normal pusher operations. and thereafter the pushers 230 are actuated in the normal sequence.

However, the master control unit is arranged to prevent the daytime mode being resumed until such time as the after treatment plant has been started up together with the separating and grinding means.

Also, the master control provides indicators such as lights to show the state of the plant, and test facilities whereby any particular operation may be manually controlled, for example, to isolate any digester and digester control for experimental manual operation or for maintenance purposes.

In setting up the plant experimental tests will enable the size of the plant, and suitable programs to be determined to suit the local conditions pertaining.

lt is to be understood that many variations and modifications of the control units described are possible to fulfill the basic requirements of determining the reaction characteristics and thereafter allocating programs or otherwise controlling the reaction conditions by controlling the supplies of water and excess air to maintain the necessary temperatures for the necessary period of time, of the order of 5 or 6 days, to bring about the substantially complete breakdown of the material, and to control the moisture content of the reacted material.

For example a single master control unit may control any required number of lines of primary plant, nd alternatively the digester control units may be incorporated with the master control unit to form an integral control means, instead of the individual digester control means being situated adjacent the respective digester and supervised by a remote master control unit. Furthermore, means may be provided to sense climatic changes such as air humidity so that the controls may be adjusted to compensate for the resultant effects upon the process, e.g. the rate of evaporation of water during the reaction. However, within the general overall temperature limits of l 10 F. to 165 F., it is desirable to keep the reaction between 140 and l60 F. and preferably at approximately 155 F. until the reaction is complete.

Provision may also be made for a signal to be supplied to the conversion device B. from a check weigher disposed in the intake to the particular digester in order that the weight may be cross-checked against the amount estimated by the master control unit in conjunction with units A. and N. the weigher and the conveyor control unit, which units are, of course, common to the group of digesters as is the data logger and the alarm system, whereas the remaining units B. to O. effectively constitute the digester control unit.

A supplementary water control unit XL. may be provided to cause supplementary amounts of water to be sprayed onto the material as it tumbles from one shelf to the next, the unit XL. being actuated in unison with the signals to the pusher control unit K., and the amount of water may be controlled by unit G.

The master control unit may incorporate a discharge-timin g unit to activate reject discharge control and to control the discharge of the digesters so that where a pivotal deflector 317 is provided, the batch to be rejected reaches the trough 313 as a discrete batch which is deflected onto the reject conveyor 318 at the appropriate time.

The control means or the master plant control unit may form part of a logistics computer which supervises the running of the whole plant, which may include the after treatment plant, and which is arranged to control the plant not only to minimize running costs but also to handle the dispatch of the resultant material to order by handling the orders, invoices, storage and the like, and such a logistics computer can be arranged to handle several lines of plant which are situated on difierent sites.

However, the use of the primary plant described has several other advantages and in particular by using a large shredder the slow feed hoppers can be made relatively small and thereby reduce to a minimum the possibility of blockages, as the hoppers need only be sufficiently large to accommodate momentary peak loads from the collection vehicles. Also the high capacity of the shredder will minimize the need for vehicles to queue or wait for space to become available for tipping.

By using a vibratory discharge conveyor particles clinging to the ferrous metal shreds will be shaken off thereby cleaning the metals, and as such metals are clean and broken up to less than a maximum size, the use of an automatic scrap-baling press is rendered attractive, and the resultant clean scrapbaled metal is suitable for reprocessing by metal manufacturers.

As a general result of the process and primary plant there is produced a fine digested product material which requires no maturing period unlike the compost material produced from rotted vegetable and like matter from refuse which afler conventional treatment requires a considerable maturing period.

ln contrast to normal compost the product material has a biological oxygen demand and a nitrogen requirement which are similar to that of soil, which the product material resembles in physical characteristics as it is biologically and physically broken down, and the product material may therefore be used as it is, for agricultural or horticultural purposes.

The stable, mature, low-moisture content and fine freeflowing form of the product material renders it suitable for immediate blending with additive materials to improve its qualities as a fertilizer, and the after treatment plant is provided for this purpose.

In the after treatment plant, the common product conveyor 306 carries the fine digested or decomposed material over a rate weigher which controls the additive blending means 4 so that the material is blended with additives according to a predetermined weight ratio.

As shown in FIGS. 8 and 9 the additive blending means comprises five hoppers 401 containing additive materials, and each hopper 401 has a constant flow discharge mechanism 402. The five discharge mechanisms 402 are linked together by proportioning controls so that the mechanisms discharge additives in accurately proportioned ratio to each other, and the proportioning controls are linked to an overall ratio controller which varies the total discharge of the additives in accordance with the rate of flow of the fine material as indicated by the rate weigher 403, and these ratios may be controlled by, for example, the logistics computer.

The additives are discharged on to the conveyor 306 through chutes 404, and the conveyor 306 deposits the material together with the additives into the first of three similar blending machines 405. Each blending machine comprises a shaped trough, indicated by reference numeral 406, and is provided with a pair of geared shafts 407 so as to be contrarotating, which shafts are provided along their lengths with helical blades, paddles or vanes (not shown), arranged so that they interdigitate and overlap between the shafts so as to propel the material along the machine and at the same time thoroughly intermixing the various constituent particles The material is passed from one blending machine 405 to the next, until the third machine 405 discharges the thoroughly blended material on to a transfer conveyor 408, of belt type.

This transfer conveyor 408 conveys the blended material to packaging and storage means 5 shown in FIG. 10, and deposits the material upon a two-level vibratory plate conveyor 501 which is similar to the vibratory conveyor 203 This vibratory conveyor 50] is arranged to feed hoppers 502 of a pair of twin bagging machines 503 which are arranged to produce large bags of fertilizer which are sealed and marked and then transferred by conveyors 504 and 505 to pal- 1. A plant for the processing of domestic refuse material comprising feeding and shredding means for shredding the entire supplied shredding material, digester means, said feeding and shredding means feeding the shredded material to said letizing machines 506, which are supplied with pallets from a digester means, said digester means comprising at least one store or respective stack 507 to produce loaded pallets which digester having a plurality of open cells, means supplying air are dispatched via conveyors 508 for loading on to transport and water to said cells to support aerobic degradation of the vehicles refuse material and control means regulating the passage of Th i r ry n y o d on m n h pthe material from cell to cell and regulating the water supply P 0f a of fe bagglhg maehlhes 509 Y h Produce to the material in the cells to at least control the moisture con- Smaller h g of fefhhlert these Smaller g g dispatched tent of the material leaving the digester, and separating and z z z t z stig z zlll' 'fi ze g g z hi ts l g h l grinding means; rzceivinfg thethmagerialdleaving thel digiesteg, Se e 8 e l 0 P e m m a removing meta o jects rom e egra ed materia an su mg a P Store 513 and dlscherglhg loaded Pallets along the sequently reducing the degraded material to fine pulverulent conveyor 15. f

y 'P material is deposited y the h y 9 to 2. A plan in accordance with claim 1, further comprising an a lhfeed conveyor 516 Whleh serves a l f Store after treatment plant having additive blending means for adg z z ht gt 3 g? mule; from es Vehlcles may ding additives to the fine pulverulent material to a total of one- 6 e u 03 3 oesel' em lzel' mate" tenth to one-third of the amounts of standard fertilizers, and

The whole of the packaging and storage means 5 is accomf h having packaging and storage means medeted in the Yecepheh building at some slight distance from 3. A plant in accordance with claim 1, wherein said feeding e Pf y Shredding feeding meahs 1 f Vehicles and shredding means comprise a fast feed hopper, a main slow bringing raw refuse material and collecting fertilizer material f d hopper and a secondary Slow feed hopper having means f ll'h safne 'g t n d h f I th 1 controlling its rate of feed so as to be proportional to the rate 5 pac 33mg may e m e or examp e of feed of the main slow feed ho er, both slow feed ho ers gistics computor, and any suitable number of silos may be prodischarging into the fast feed gg pp vided to store difierent additive blends. Initially, the additives A plant in accordance with claim 3 wherein feeding and g fhi fggili'ge ggg? 2g fi zgj ig i' gfiz 5:22:: shredding means further comprise a primary shredder having i' oduct material the ee ted necessa amounts foifnd in atlcias-t horse power per 109 per day plant omput E Sm d d f p f m 2' otassh and wherein said separating and grinding means further comprise 2 te at s 1 5;: g r g fgz a secondary grinding or crushing machine having at least 100 5 5:2; 0 pt 8 horsepower per 100 tons per day plant output.

5. A plant in accordance with claim 4, further comprising g galh ig s g h s notdnecesssrytand 35 safety means having a metal detector disposed adjacent said t i t g a Cou 6 ms [ca y re Ce fast feed hopper for halting said primary shredder when an abthirds to more than nine-tenths depending upon circumnormally large piece ofmetal is dammed $2 5; 8 whlk: i :r.:; g g y g tz gg 2x2: 6. A plant in accordance with claim I, wherein said separatf fs 355 p n q ing and grinding means further comprise an automatic maglgnoring the individual proportions of the additives, the sum 40 F for magnetic .matenais from the digested material; a tin baler for baling said materials, a metal total thereof added to said produce material is generally less dete tor a d Se armor for removi etals METALS f than one-tenth of the equivalent total found in the relevant th 52 t m sec d 59 standard fertilizer, which gives great commercial savings. e f' i i i i Sc r on i gnn mg In particular, the following tables I and Il show amounts of l c me a a VI 2 2 y I additives (expressed in terms of percentage weight of active p an accor ance i gremdsal comm constituents); table I being for two known standard fertilizers gl compnsle a con 0 s: a seParate and table ll being for two generally comparable enriched fer- $3 com?) or a W F tilizer materials with a further example all being produced master p am comfo master p am comm being adapted to provide a daytime mode of plant operation from the said product material. f

While the first and second examples of the tables are comand an ahemauve mghmme m )de? operauon also bemg parable, in that when applied at the same weight of material adapmd comm] the and batchmg of the per unit area of land they produce equivalent results, this is Shredded mzftenal fed to means and the Passage not to say that the materials are identical under all circum- Ofthe hrough dfgestel: means' stances; but on average the results will be generally indistin- A Plant aFcol'dance wlthflalm f" guishable and no repeatable exceptions have been found. means comprise a l l vibratory plate conveyor, said The additives may be in any Suitable form bone meal, master plant control unit controlling said plate conveyor so as fish meal, chemical products, crushed minerals, blended as 9 feed predetermined amounts the matel'lal each described, and compounded as necessary in accordance with dlgeslert Said p e Conveyor eomphslhg a P h' y of upper procedures described herein. plates and a plurality of lower plates, a respective one of said TABLE I Fertiliser type Phosphate} Phosphate/ Approx. Nitrogen soluble insoluble Potassium total Grass crops, etc 5.0 1. 2 4.5 8. 5 14. 2 Root crops, etc 6. 0 4. 5 1. 0 5. 0 16. 5

TABLE II Fertiliser typo Phosphate/ Phosphate] Approx. Nitrogen soluble insoluble Potassium total Lawns, etc 0.6 0.02 0.3 0.12 1. 0 Kitchen gardens, etc 0. 0.28 0. 3 0.35 1. 0 Rose beds 0.95 0. 25 0. 3 0.53 2. 0

lower plates being recessed where it overlies the inlet of the digester to distribute the material into the digester, said digester means further comprising a jigging plate conveyor receiving the material from each digester.

9. A plant in accordance with claim 1, wherein said control means comprise sensors for sensing the temperature of the material within the cells, said control means regulating the moisture content in each cell to control the digestion, degradation and breakdown of the material, the air supply being at least sufficient to ensure aerobic conditions in the cells 10. A plant in accordance with claim 9, wherein each digester of said digester means comprises a plurality of alternately superimposed shelves defining said cells, whereby said cells are superimposed and intercommunicating, said shelves extending with a downward slope alternately from two opposed walls of the digester, said control means being provided for each shelf to progress the material down each shelf, whereby the material eventually falls upon the shelf below, said air and water-supplying means comprising water sprays to moisten the material on each shelf, air supply lines to aerate the material on each shelf and temperature probes for sensing the temperature of the material on each shelf.

11. A plant in accordance with claim 9, wherein said control means cause predetermined amounts of air and water to be supplied to the material in a test area adjacent the inlet of the digester to sense the resultant material temperature, a reaction characteristic for the material being derived therefrom, said control means comprising a program selector and actuator for selecting a program from the reaction characteristic, the supply of air and water to the material as it progresses through the digester being controlled thereafter in accordance with the selected program.

12. A plant in accordance with claim 11, wherein the control means actuating the means for progressing the material through the digester comprise summation and conversion units for recording the progression of the material, said program actuator being responsive to signals from said conversion unit to keep the program in phase with the progression of the material.

13. A plant in accordance with claim 11, having a product reject control unit, said program selector and actuator being adapted to actuate said product reject control unit to cause any batch of the material which has an unsatisfactory reaction characteristic to be rejected as it leaves the digester said pro gram selector and actuator being further adapted to respond to a feedback loop from further temperature probes to select a modified program should the temperature of the material vary beyond predetermined limits.

i t I I 

1. A plant for the processing of domestic refuse material comprising feeding and shredding means for shredding the entire supplied shredding material, digester means, said feeding and shredding means feeding the shredded material to said digester means, said digester means comprising at least one digester having a plurality of open cells, means supplying air and water to said cells to support aerobic degradation of the refuse material and control means regulating the passage of the material from cell to cell and regulating the water supply to the material in the cells to at least control the moisture content of the material leaving the digester, and separating and grinding means receiving the material leaving the digester, removing metal objects from the degradeD material and subsequently reducing the degraded material to fine pulverulent form.
 2. A plan in accordance with claim 1, further comprising an after treatment plant having additive blending means for adding additives to the fine pulverulent material to a total of one-tenth to one-third of the amounts of standard fertilizers, and further having packaging and storage means.
 3. A plant in accordance with claim 1, wherein said feeding and shredding means comprise a fast feed hopper, a main slow feed hopper and a secondary slow feed hopper having means controlling its rate of feed so as to be proportional to the rate of feed of the main slow feed hopper, both slow feed hoppers discharging into the fast feed hopper.
 4. A plant in accordance with claim 3, wherein feeding and shredding means further comprise a primary shredder having at least 100 horse power per 100 tons per day plant output and wherein said separating and grinding means further comprise a secondary grinding or crushing machine having at least 100 horsepower per 100 tons per day plant output.
 5. A plant in accordance with claim 4, further comprising safety means having a metal detector disposed adjacent said fast feed hopper for halting said primary shredder when an abnormally large piece of metal is detected.
 6. A plant in accordance with claim 1, wherein said separating and grinding means further comprise an automatic magnetic separator for removing magnetic materials from the digested material, a tin baler for baling said materials, a metal detector and separator for removing non-ferrus metals from the digested material, a primary screen, a secondary grinding or crushing machine and a vibratory secondary screen.
 7. A plant in accordance with claim 1, wherein said control means comprise a master plant control unit and a separate digester control unit for each digester which is responsive to said master plant control unit, said master plant control unit being adapted to provide a daytime mode of plant operation and an alternative nighttime mode of operation and also being adapted to control the distribution and batching of the shredded material fed to said digester means and the passage of the material through said digester means.
 8. A plant in accordance with claim 7, wherein said digester means comprise a two level vibratory plate conveyor, said master plant control unit controlling said plate conveyor so as to feed predetermined amounts of the material to each digester, said plate conveyor comprising a plurality of upper plates and a plurality of lower plates, a respective one of said lower plates being recessed where it overlies the inlet of the digester to distribute the material into the digester, said digester means further comprising a jigging plate conveyor receiving the material from each digester.
 9. A plant in accordance with claim 1, wherein said control means comprise sensors for sensing the temperature of the material within the cells, said control means regulating the moisture content in each cell to control the digestion, degradation and breakdown of the material, the air supply being at least sufficient to ensure aerobic conditions in the cells.
 10. A plant in accordance with claim 9, wherein each digester of said digester means comprises a plurality of alternately superimposed shelves defining said cells, whereby said cells are superimposed and intercommunicating, said shelves extending with a downward slope alternately from two opposed walls of the digester, said control means being provided for each shelf to progress the material down each shelf, whereby the material eventually falls upon the shelf below, said air and water-supplying means comprising water sprays to moisten the material on each shelf, air supply lines to aerate the material on each shelf and temperature probes for sensing the temperature of the material on each shelf.
 11. A plant in accordance with claim 9, wherein said control means cause predetermined amounts of air and water tO be supplied to the material in a test area adjacent the inlet of the digester to sense the resultant material temperature, a reaction characteristic for the material being derived therefrom, said control means comprising a program selector and actuator for selecting a program from the reaction characteristic, the supply of air and water to the material as it progresses through the digester being controlled thereafter in accordance with the selected program.
 12. A plant in accordance with claim 11, wherein the control means actuating the means for progressing the material through the digester comprise summation and conversion units for recording the progression of the material, said program actuator being responsive to signals from said conversion unit to keep the program in phase with the progression of the material.
 13. A plant in accordance with claim 11, having a product reject control unit, said program selector and actuator being adapted to actuate said product reject control unit to cause any batch of the material which has an unsatisfactory reaction characteristic to be rejected as it leaves the digester, said program selector and actuator being further adapted to respond to a feedback loop from further temperature probes to select a modified program should the temperature of the material vary beyond predetermined limits. 